The long-term objective of this project is to understand the mechanisms underlying the development and termination of the CD4 T cell arm of the immune response. These are fundamental processes with potentially wide health-related implications, from comprehending the normal immune response to grasping the possible consequences of a failure to eliminate activated T cells, such as autoimmune disease. Naive T cells undergo clonal expansion and differentiation in response to antigen, then exert their effects primarily through the secretion of cytokines. Subsequently, it is necessary to restore homeostasis by deleting this large population of activated cells by apoptosis. Caspase 7, a member of a family of proteases known to be important for cell death, is activated in apoptotic cells, though little is known of its function. Surprising preliminary data shows that not only are caspase 7 knockout T cells partially resistant to apoptosis, but they also fail to secrete interferon gamma, an important effector cytokine, and produce reduced amounts of IL-2, a cytokine important for both T cell proliferation and apoptosis. The candidate proposes to further study the role of caspase 7 in T cell cytokine secretion and apoptosis. In vitro studies of proliferation and cytokine production in caspase 7 deficient T cells, and in vivo immunologic challenge, will further test the hypothesis that caspase 7 is important for T cell function. A mechanistic link between caspase 7 and cytokine secretion will be sought by determining its effects on signaling pathways that influence cytokine production and by identifying its substrates with two approaches: mass spectrometry of differences in protein cleavage between wild type and knockout T cells; and yeast two-hybrid screening. The role of caspase 7 in T cell apoptosis will be approached by determining the effects of its combined deficiency with caspase 3, a highly related protease that is important, but not necessary, for apoptosis. The applicant is completing a fellowship at Yale University in Pediatric Critical Care, and will continue there as a junior faculty member. The proposed research will be done in the Department of Immunobiology, an ideal location for research training due to quality faculty, strong mentorship, breadth of research topics and outstanding facilities. This K08 award will greatly assist his research into apoptosis and T cell immunology, and provide him with time and resources to develop into an independent basic science investigator.